I have 2 full sized child booster seats (Safe n Sound Maxi-Riders) in the back of my XR5 and there is plenty of room for the kids to get in/out on their own. No probs leaning in to fasten their seatbelts either.
Fuel economy is how you use your right foot - but I had just under 10L/100kms for my first 500kms. Thats some driving around Sydney, plus the first leg from Sydney to Canberra. I think around town, it is around 12's, depending on how many traffic lights you have. I'll be trying to go for a proper blast now that I am up to 1000kms